Measles is becoming more contagious
The rate of spread of the measles virus in the United Kingdom is increasing, a study suggests.
Researchers used data from recent measles outbreaks in England and Wales
to measure the reproductive number of the virus, which is the average
number of new infections that an infected person causes.
They report that the reproductive number has risen from a value of 0.47
for the years 1995–98 to a value of 0.82 for the years from 1999–2002.
The researchers point out that if the reproductive number exceeds a value
of one, then the virus will not disappear after each outbreak, but may
become a self-sustaining or endemic disease. “We are approaching
the danger zone where measles could once again become an endemic disease
in the United Kingdom. We are not yet there, but it may be going that
way,” said Dr Vincent Jansen, one of the authors of the paper.
It is not known whether the drop in infant measles, mumps and rubella
(MMR) vaccination uptake is responsible for this phenomenon, although
the reproductive number is approximately proportional to the fraction
of the population that is not immunised. “Of course the coincidence
is suggestive of a causative connection, but we cannot draw this conclusion
from our data,” Dr Jansen added (Science 2003;301:804). |
